1. Field of the Disclosure
This disclosure generally relates to three-dimensional (3D) woven preforms and particularly relates to 3D woven preforms used in reinforced composite materials. More particularly, the present disclosure relates to preforms that can be formed into a “T” shape. More particularly still, the present disclosure relates to preforms that can be formed into a “T” shape with formed gaps that are filled with integrated material.
2. Related Art
The use of reinforced composite materials to produce structural components is now widespread, particularly in applications where their desirable characteristics of light weight, high strength, toughness, thermal resistance, and ability to be formed and shaped can be used to great advantage. Such components are used, for example, in aeronautical, aerospace, satellite, high performance recreational products, marine, and other applications.
Typically, such components consist of reinforcement materials embedded in a matrix material. The reinforcement component may be made from materials such as glass, carbon, ceramic, aramid, polyethylene, and/or other materials which exhibit desired physical, thermal, chemical and/or other properties, chief among which is great strength against stress failure. These materials are often fabricated into fibers and used as reinforcing fibers, or the fibers are formed into yarns which are used as reinforcing yarns in the component.
Through the use of such reinforcement materials, which ultimately become a constituent element of a completed component, the desirable characteristics of the reinforcement materials, such as very high strength, are imparted to the completed composite component. The typical constituent reinforcement materials may be woven, knitted, braided, laminated or otherwise oriented into desired configurations for reinforcement preforms. In many cases, particular attention is paid to ensure the optimum utilization of the properties for which the constituent reinforcing materials have been selected. Usually such reinforcement preforms are combined with matrix material to form desired finished components or to produce working stock for the ultimate production of finished components.
After the desired reinforcement preform has been constructed, a resin or matrix material may be introduced to and into the preform, so that typically the reinforcement preform becomes encased in the matrix material and matrix material fills the interstitial areas between the constituent elements of the reinforcement preform. The matrix material may be any of a wide variety of materials, such as epoxy, bismaleimide, polyester, vinyl-ester, ceramic, carbon and/or other materials, which also exhibit desired physical, thermal, chemical and/or other properties. The materials chosen for use as the matrix may or may not be the same as that of the reinforcement preform and may or may not have comparable physical, chemical thermal or other properties. Typically, however, they will not be of the same materials or have comparable physical, chemical, thermal, or other properties, since a usual objective sought in using composites in the first place is to achieve a combination of characteristics in the finished product that is not attainable through the use of one constituent material alone. So combined, the reinforced preform and the matrix material may then be cured and stabilized in the same operation by thermosetting or other known methods, and then subjected to other operations toward producing the desired component. It is significant to note at this point that after being so cured, the then solidified masses of the matrix material normally are very strongly adhered to the reinforcing material (e.g., the reinforcement preform). As a result, stress on the finished component, particularly via its matrix material acting as an adhesive between fibers, may be effectively transferred to, and borne by, the constituent material of the reinforcement preform. Any break or discontinuity in the reinforcement preform limits the ability of the preform to transfer and bear the stress applied to the finished component.
In certain applications, three dimensional (3D) woven composite structures are desired as primary load carrying members. One useful shape of a preform for such members is generally referred to as a “T” preform, so called because it resembles the letter T in an axial view. Other useful preforms may have different cross sectional shapes, such as Pi (π), H, I, or L for example. Fiber preforms with specific structural shapes can be woven on a conventional shuttle loom, and several existing patents describe the method of weaving such structures.
One of the drawbacks of the use of these preforms is that they form gaps when they are bifurcated or divided. These gaps are usually filled according to conventional methods by adding additional material to the preform. But filling the gap with added material removes the overall continuity of the preform. Further, requiring the addition of new material adds labor, materials, and cost to the preform manufacture. Finally, the added material is not integrally connected to the preform, which reduces the structural integrity of the preform.
To maintain the structural integrity of the preform, in many cases the addition of reinforcements is required at the gap. The reinforcement is often in the form of sheets of material, typically additional woven material. The additional reinforcement creates a localized increase in thickness and weight of the preform. The reinforcement may create a localized weight concentration in the reinforced gap itself.
Other known methods may require mechanical fasteners, for example, bolts or rivets, to affix the reinforcement to the preform at the gap. However, the use of metal bolts or rivets at the interface of such components is often unacceptable because such fasteners require through holes which further compromise the integrity of the composite structure. Detrimentally, fasteners add weight and introduce different coefficients of thermal expansion as between such elements and the surrounding material.
Prior art methods have not adequately addressed the need for 3D woven preforms able to be formed into gap fillers without the addition of other materials and the resultant increase in localized thickness and additional weight. The present disclosure addresses the shortcomings of the prior art by providing a 3D woven preform with its gaps filled with integrated material without the need for additional material with an associated increase in localized thickness additional weight and decrease in structural integrity.